It depends. A lot of firmware updates are delayed or just blocked by the carriers. Every Nokia phone has a ID code, different carriers have their own code, so can control the release (or not) of firmware updates. Even "unbranded" phones in the UK do not have a generic ID code, they have a UK CV (Country variant) code, which again is subject to a delay, although nobody seems to know what faceless bureaucrat is responsible for giving firmware releases a thumbs up for the UK CV models.
This is why I change the ID codes of all my Nokia phones to that of a generic Euro one. Unfortunately talk of doing such things is forbidden on the Nokia discussions forums, which is a pity as most of the complaints seem to centre around "Where is version xxx for my phone" and complaints of bugs which are resolved in a firmware release the victim isn't privy to.
I recently used my original N95-1 (not an unpleasant experience), and was amazed to find a firmware update for it was issued this year!
I think it only added the OVI store, but it was nice it wasn't forgotten.
I don't think the problem is long term support, I think the problem is they got caught slacking a bit and now they are rushing things out the door and not testing them properly before they are released.
Then again, maybe this isn't such a new thing. I remember the N95 was slated for it's battery life and various other issues when it first came out with early firmware... A few months down the line, a few firmware updates, and there was nothing wrong with it.
Just hope the same can be said for my N97!